#define _CRT_SECURE_NO_WARNINGS 1

#include <stdio.h>
int main()
{
	int n = 0;
	int arr[9] = { 1,2,3,4,5,4,3,2,1 };
	for (int i = 0; i < 9; i++)
		n = n ^ arr[i];
	printf("%d\n", n);
	return 0;
}